ABSTRACT: The effects of the therapist's behavior on the process and outcome of brief dynamic psychotherapy will be investigated. We shall study in a case-specific way how a therapeutic intervention affects the patient during the therapy session and how these individual "session effects" may produce a positive or negative outcome. A conceptual framework (called control-mastery theory) for evaluating the relevance of therapist interventions to the problems and needs of particular patients is described. The concept of the patient's treatment plan is central to the control-mastery theory. The patient's plan, which can be assessed reliably, includes the patient's goals, the obstructions to attaining them, and the means by which the patient will work to achieve them; the means are tests performed by the patient on the therapist--the patient tests the therapist in order to overcome pathogenic beliefs. When the therapist passes an important test, the therapeutic work gains momentum; when he fails a test the patient becomes constricted. The immediate effects of passing or failing a patient's tests will be assessed. We hypothesize that passed tests will be significantly with an increase in the patient's level of therapeutic boldness, relaxation, and involvement. Our second aim is to demonstrate that there is a positive relationship between the degree to which tests are passed and treatment outcome (as assessed by standard measures such as Target Complaints, SCL 90, GAS, and a case-specific measure of outcome called plan attainment). Patients in the study will be 20 adult outpatients for whom brief therapy is indicated. The therapists will be 10 psychodynamically-oriented psychologists and psychiatrists with at least three years of therapy experience.